A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In recent developments, an increased problem of providing thermally stable articles, such as a substrate to be targeted with a patterned beam or a reticle, occurs due to ever more demanding requirements for image resolution, in particular in the new field of immersion lithography. Here, thermal stabilization is difficult, since an immersion liquid may cause thermal cooling by transitioning to a vapor phase. Hence, a considerable local thermal gradient may occur in the article that needs to be stabilized. Also or alternatively, during a photolithographic treatment of an article, the article, due to subsequent illuminations of target portions, tends to be warmed up unevenly. This unevenness may cause a thermal gradient which causes a local deformation of the article. For nanometer projection accuracy, this may cause a problem resulting in focus and/or overlay errors. That is, due to thermal deformation, the surface of the substrate and/or reticle bends away from an ideal projection plane, which may result in focus loss or at least an effective sideways movement of the image plane so that an overlay problem may occur.